Identification of novel Ah receptor agonists using a high-throughput green fluorescent protein-based recombinant cell bioassay.

The Ah receptor is a ligand-dependent transcription factor that mediates the biological and toxic effects of polycyclic aromatic hydrocarbons and halogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin). Recent evidence also suggests a role for the AhR in normal physiology and development. Although a variety of structurally diverse chemicals are reported to bind to and activate the AhR, the full spectrum of structural chemical classes that can interact with the AhR remains to be elucidated. Large-scale analysis of the ligand binding specificity of the AhR requires the use of a high-throughput AhR bioassay system for chemical screening. We have utilized a recombinant mouse hepatoma cell line (H1G1.1c3) containing a stably integrated TCDD- and AhR-responsive enhanced green fluorescent protein (EGFP) reporter gene to screen a 1,5-dialkylamino-2,4-dinitrobenzene combinatorial chemical library consisting of 155 parental amines and up to 12 090 combinatorial products in less than 7 days for novel AhR agonists. These analyses have identified numerous parental amines as relatively potent inducers of EGFP (with EC(50)s between 8 and 1000 microM) and also have revealed several novel products of the combinatorial chemical library synthesis with EC(50)s between 10 and 100 microM. Overall, these results have not only allowed the identification of novel activators of the AhR but also demonstrate the utility of the recombinant H1G1.1c3 cell bioassay for high-throughput chemical screening.